The invention relates to a static mixer with precision cast elements arranged along a central axis, to a cast element for a mixer of this kind, and to a method for manufacturing the mixer as well as to uses.
A static mixer by means of which highly viscous polymer melts can be homogenized is known from Signer U.S. Pat. No. 5,564,827. This mixer can be used as a mixer head in the nozzle of an injection molding machine or as a melt mixer following the helix of an extruder. It is assembled from cast elements and intermediate elements and has a cylindrical shape. The cast elements contain structures, for example grid structures, which effect a mixing process in a through-flowing melt. The structures which are shown in Signer U.S. Pat. No. 5,564,827 are built up of layers which contain passages and which are oriented parallel to a central axis. In a preferred embodiment the intermediate elements together with parts of the cast elements, namely with flange-like reinforcing rings, form a tubular jacket, within which a plurality of mixer structures are arranged one behind the other. In adjacent mixer structures the layers are in each case displaced with respect to one another by a predetermined angle, preferably by 90xc2x0. In order that this displacement is reliably produced in the assembly of the static mixer, cams are molded on the reinforcing rings and cut-outs are provided at the intermediate elements in a manner which is complementary to the cams. In a correct assembly the cams fit into the corresponding cut-outs and thus provide for a predetermined orientation of the elements.
The cast elements can be manufactured by means of precision casting to within tolerances of 0.1 mm. For use in injection molding machines this tolerance is insufficient. Because of the sealing, a total length of the static mixer which is to be strictly observed is required in machines of this kind.
The object of the invention is to further develop the static mixer of the named embodiment in such a manner that, a predetermined total length of the mixer, such as for example is required in injection molding machines, can be manufactured precisely.
The static mixer contains precision cast elements which are arranged along a central axis and which in each case have a reinforcement region at their circumference which extends over the entire circumference. These cast elements are assembled with intermediate elements to form a cylindrical body. Joint locations between the elements form surfaces which stand transversely to the central axis. For each isolated cast element, in a rotation about its central axis, the joint locations are accessible to machining tools for subsequent machiningxe2x80x94in particular for grinding or turning. As a result of the subsequent machining a predetermined total length of the mixer in the direction of the central axis can be precisely achieved.
In the known cast elements a required subsequent machining is made impossible due to the cams at the reinforcing rings. In the intermediate elements a subsequent machining is not required since the latter can be brought into a predetermined shape from a tube by a cutting method, with it being possible to produce the required precision.